Sporadic inclusion-body myositis (s-IBM) is a progressive, highly debilitating, and the most common muscle disease of older persons (over age 60). An intriguing aspect of s-IBM is that its muscle fiber phenotype has features remarkably similar to those of Alzheimer Disease (AD) brain ("IBM-AD phenotype"), including abnormal accumulations of: beta-amyloid precursor protein (betaAPP) and of several other proteins accumulated in AD brain. Another similarity to AD is the presence of hereditary forms, termed "hereditary inclusion-body myopathies (h-IBM)", which clinically are manifest earlier than s-IBM, but have a muscle- fiber phenotype identical to, though apparently somewhat less advanced than, that of s-IBM. Similarly to AD brain, abnormal muscle fibers of s- and h-IBM muscle, in vivo and in vitro. Therefore, we propose that betaAPP over-expression (whole molecule and/or Abeta fragment in the milieu of aged (s-IBM) or genetically-abnormal adult (h-IBM) muscle fibers causes molecular disturbances leading to the IBM-specific vacuolar muscle-fiber degeneration and expression of the IBM-AD phenotype. This proposal addresses the schedule, and therefore the possible mechanisms, of the early steps in the pathogenic cascade. It involves: 1) three long-term in vitro models, namely, a) spontaneous model utilizing cultures of s-IBM muscle; and cc) an induced model utilizing matured cultured normal human muscle fibers into which is transferred the betaAPP gene; and 2) an induced in vivo aged-rat model based on transfer of the betaAPP gene into aged-rat gastrocnemius muscle. Anti-oxidant treatments, including estrogens, will be done on abnormal cultures. We postulate that in vivo aging of the involve tissues may be a predisposing factor(s) in both the AD group and the IBM's, especially in the sporadic, more common, forms of each. Because our type of cultured spontaneous and induced models of the human tissue actually affected in the patient are not available to study brain involvement in the AD's, possibly our results may provide otherwise- unavailable information relevant to the pathogenesis and treatment of the AD's.